Speaking to the BBC, he said: "Please show him some mercy and understand he is a humanitarian aid worker. He's not a fighter, he's not come there for no political reasons, he's come there strictly to help the people."

And now more than 100 Muslim leaders have signed a statement to IS pleading for his release and criticising them as "monsters" for the brutal murder of Mr Haines.

"We, the undersigned British Muslim Imams, organisations and individuals, wish to express our horror and revulsion at the senseless murder of David Haines and the threat to the life of our fellow British citizen, Alan Henning," said the leaders in a letter published in the Independent.

They said those holding Mr Henning hostage must accept that what they are doing is against the Koran and "constitutes the worst condemnable sin".

In another online appeal, Abu Bakr al-Baghdadi, representing British Muslim aid workers, told of the various ways Mr Henning had raised money to bring to Syria, having been moved by the plight of people there.

In an emotional speech to the camera, Mr al-Baghdadi said: "You have the ability to spare the life of this innocent man. We beg you to tread the path of justice and show him the compassion that Allah has placed in the hearts of the believers and in your heart."